Unraveling the Influence of Oxygen Vacancies on the OER Performance of Co Single-Atom Catalysts Adsorbed on MXenes

Abstract

Toenable efficient energy conversion and storage, the developmentof effective electrocatalysts for the oxygen evolution reaction (OER)is crucial. Single-atom catalysts (SACs) with 100% active sites forthe OER are highly promising in this regard. In this study, we investigatedthe OER activities of Co single atoms (Co-SA) adsorbed onmetallic MXenes, including Ti3C2O2 and Mo2CO2, both in their stoichiometric formand with oxygen vacancies (O-v), using spin-polarized first-principles-basedcalculations. The rate-determining step in each case was found tobe the conversion of *O from *OH. Our calculations showed that thepresence of oxygen vacancies decreased the OER activity in Co-SA@Ti3C2O2-& delta;,resulting in a higher overpotential, while it increased the OER activityin Co-SA@Mo2CO2. We explain such resultsusing insights from the density of states, charge density variation,and bonding analysis via crystal orbital Hamilton population. We alsoshow that the hybridization between the d-states of the Co-SA and the transition metal sites of the catalyst-bed (Ti/Mo) playsa decisive role.